1. Field of the Invention
The present invention relates to the field of illumination equipments, and more particularly to a ceiling lamp adopting a non-separating driver circuit, and a non-separating power converter is operated having a linear constant current output controller to improve the overall operating efficiency of the lamp and complies with the energy saving and environmental protection requirements.
2. Description of the Related Art
To create a comfortable, bright and stylish reading space or working space, fashionable ceiling lamps are generally installed to the ceiling as shown in FIG. 1, and the ceiling lamp 1 generally comprises a lamp disc 10, a heat dissipating plate 11, a lamp panel 12, a reflecting cover 13 and a lamp cover 14, and the lamp disc 10 is provided for installing and stacking the heat dissipating plate 11 and the lamp panel 12, and the lamp panel 12 has a driver circuit (not shown in the figure) and a plurality of light emitting diodes (LEDs) 120 installed around the periphery of the lamp panel 12 as shown in FIGS. 2 to 4, and the driver circuit adopts a switching power converter as the main circuit architecture and the switching power converter is generally a fly-back, forward, push-pull, half-bridge or full-bridge circuit. The reflecting cover 13 is covered onto the middle position of the lamp panel 12 and sealed into the lamp cover 14, so that the reflecting cover 13 can enhance the effect of diffusing the light source emitted from the LEDs to expand the illumination range of the ceiling lamp 1. In FIG. 2, the driver circuit adopts the fly-back converter 121 as the main power structure, and a pulse width modulation (PWM) control method is used to adjust the power intensity of an operating current (Io) outputted to the LEDs 120 to allow the ceiling lamp 1 to operate at a constant current and a constant power, so as to provide a stable illumination quality to users. However, such conventional fly-back converter 121 outputs an operating current with the drawbacks of a relatively larger ripple waves, a relatively lower precision of load adjustment, and relatively more strobes produced by a PWM dimming and a relatively greater electromagnetic interference (EMI), so that it is necessary to install an EMI filter additionally to avoid contaminating the power source of the utility power or affecting the using quality of the remaining electronic products, and thus resulting in a higher manufacturing cost of the lamp panel 12.
In addition, the driver circuit can adopt a power factor (PF) correction single-stage fly-back converter 122 as the main power source structure as shown in FIG. 3, and then a negative booster 123 is installed at an output terminal. The single-stage fly-back converter 122 has a transformer 1220 with a primary side coil (NP), a secondary side coil (NS) and an auxiliary coil (NA), and the primary side coil is electrically coupled to a bridge rectifier 1221, and the primary side coil and the auxiliary coil are electrically coupled to a power factor control IC (FPC IC) 1222. The secondary side coil is electrically coupled to the LEDs 120 through an output inductor 1230, and the secondary side coil and the output inductor 1230 are electrically coupled to a DC/DC IC 1223, and the output inductor 1230 is electrically coupled to the FPC IC 1222 through a photocoupler 1224. The single-stage fly-back converter 122 uses the transformer 1220 to convert an input voltage rectified and outputted by the bridge rectifier 1221, and then the output inductor 1230 steps down the voltage to produce an operating voltage required by the LEDs 120. In the meantime, the single-stage fly-back converter 122 uses the photocoupler 1224, the DC/DC IC 1223 and the FPC IC 1222 to monitor the output voltage value of the operating voltage, so as to control the operating cycle of the primary side coil that affects the voltage value outputted by the secondary side coil, and ensure the effect of outputting the operating voltage stably. Since the main circuit architecture of this driver circuit integrates the power factor correction function and the DC/DC control function without requiring the installation of other control devices, so as to achieve the effect of lowering the cost. However, after the input voltage has a first-time energy conversion through the transformer 1220, it is necessary to have the output inductor 1230 to perform a second-stage conversion before the required operating voltage can be outputted, so that more ripples are produced when the energy conversion efficiency is low and the value of the outputted operating voltage is small.
In FIG. 4, the driver circuit comprises a PFC double-stage fly-back converter 124 and a negative booster 125, wherein a front stage and a back stage are defined between a primary side coil and a secondary side coil of a transformer 1240, and the front stage includes an input inductor 1241 and a FPC IC 1242, wherein the FPC IC 1242 is provided for checking an input current and an output voltage of the front stage before switching a first switch 1243 ON or OFF to regulate the conduction cycle of the input inductor 1241 to change the intensity of a current generated by the primary side coil, so as to affect the intensity of a current outputted from the secondary side coil. In addition, the back stage includes a DC/DC IC 1244 for checking the intensity of a current outputted by the secondary side coil to change the state of the second switch 1245 to regulate the conduction cycle of an output inductor 1250, so as to eliminate the ripple amplitude of the outputted operating voltage. Therefore, the driver circuit can provide a ripple-free operating voltage with a very high stability to improve the illumination quality of the ceiling lamp 1. However, after the input voltage is boosted by the input inductor 1241, the voltage is converted by the transformer 1240 and then stepped down and outputted by the output inductor 1250. In other words, the input voltage is processed through a three-stage conversion before the required operating voltage can be obtained, and thus resulting in a high power loss and low power conversion efficiency, and incurring a high cost for a complicated circuit architecture. Obviously, the conventional ceiling lamp is not conductive to industrial development and applications.
In view of the aforementioned problems, it is a main subject of the present invention to improve the circuit architecture of the driver circuit by providing a very stable operating voltage to the LEDs 120, while improving the conversion efficiency and simplifying the complexity of the driver circuit to lower the cost.